For automobiles and the like, there is a demand for improvements of the fuel efficiency (fuel consumption) of internal-combustion engines, not only to cope with environmental issues and comply with exhaust emission regulations, but also to meet the increase in awareness of energy conversion and prevent resource depletion. Therefore, the combustion efficiency of internal-combustion engines is increased to reduce the fuel used in combustion, and further, the hazardous components in emissions are reduced.
As an example for increasing the combustion efficiency of an internal-combustion engine, a valve timing control (VTC) device is known. The valve timing control device optimizes the timings to open and close the inlet valve and the outlet valve based on the engine speed and the intake air quantity (load) of the internal-combustion engine. This valve timing control device includes a hydraulic mechanism that rotates a camshaft in a relative manner, and controls the position of a hydraulic control valve that uses an electromagnet. In this manner, the oil quantity of the hydraulic mechanism is adjusted so that the timings to open and close the inlet valve and the outlet valve are changed.
Other than the valve timing control device, a gearshift control valve that is used in an automatic transmission, an electronic throttle control device provided in an air intake passage, or the like is used to improve fuel efficiency. Such devices have electromagnets and motors as principal drive sources, and are driven and controlled by electrical power supplied to magnet coils. In view of the above, a magnet coil drive control device that controls power to be supplied to an electromagnet or the magnet coil of a motor is essential in operating the mechanical part of an automobile.
For example, in a drive control device for driving a magnet coil according to JP 2006-35910 A (PTL 1), a low-side switch is provided for the magnet coil, and the current and the like flowing into the magnet coil are controlled by opening and closing this switch. PTL 1 discloses a method of shortening the time of attenuation of inductive current generated in the magnet coil, so as to restrain increases in the temperature of the magnet coil.